ISAR imaging Based on the Empirical Mode Decomposition Time-Frequency Representation

International audienceThis work proposes an adaptation of the Empirical Mode Decomposition Time-Frequency Distribution (EMD-TFD) to non-analytic complex-valued signals. Then, the modified version of EMD-TFD is used in the formation of Inverse Synthetic Aperture Radar (ISAR) image. This new method, referred to as NSBEMD-TFD, is obtained by extending the Non uniformly Sampled Bivariate Empirical Mode Decomposition (NSBEMD) to design a filter in the ambiguity domain and to clean the Time-Frequency Distribution (TFD) of signal. The effectiveness of the proposed scheme of ISAR formation is illustrated on synthetic and real signals. The results of our proposed methods are compared to other Time-Frequency Representation (TFR) such as Spectrogram, Wigner-Ville Distribution (WVD), Smoothed Pseudo Wigner-Ville Distribution (SPWVD) or others methods based on EMD

Détection, localisation et identification de cibles radar par imagerie électromagnétique bistatique

The purpose of this work is to develop, characterize and analyze the bistatic imagery radar. In our study, we consider in the general case of a bistatic configuration without configuration condition. Then, we develop an image processing valid in all acquisition configurations and which takes into account the emission and reception polarizations. Thus, we can characterize the obtained images and give the expression of the bistatic image resolutions according to the acquisition configuration. Then, we study the bistatic images obtained for complex targets and target detection on oceanic surface in order to compare the results obtained with those of a monostatic configuration. The results obtained make it possible to validate the bistatic configuration interest and to present new prospects offers by this subject.L'objectif de cette thèse est de développer, caractériser et analyser l'imagerie radar en configuration bistatique. Dans le cadre de notre étude, nous nous plaçons dans le cas général d'une configuration bistatique sans condition sur la configuration d'acquisition. Nous avons alors développé un algorithme de reconstruction d'images tenant compte des polarisations d'émission et de réception. Ainsi, nous avons pu caractériser les images obtenues et donner l'expression des résolutions d'une image bistatique en fonction de la configuration d'acquisition. Ensuite, nous avons étudié les images bistatiques reconstruites lors de l'observation de cibles complexes ainsi que celles obtenues lors de la détection de cibles sur une surface océanique afin de les comparer avec celles d'une configuration monostatique. Les résultats ainsi obtenus permettent de valider l'intérêt de la configuration bistatique et de présenter les nouvelles perspectives qu'offre ce sujet de recherche en imagerie radar

Détection, localisation et identification de cibles radar par imagerie électromagnétique bistatique

Les travaux présentés dans ce manuscrit sont consacrés à l'étude de l'imagerie radar bistatique. Nous considérons le cas général d'une liaison radar bistatique pour laquelle l'émetteur, la cible et le récepteur peuvent être en mouvement. Le modèle tri-dimensionnel développé prend en compte l'ensemble des éléments de la chaîne d'acquisition ainsi que les polarisations d'émission et de réception. L'algorithme développé pour la reconstruction des images bistatiques est une extension de l'algorithme RDA (Range Doppler Algorithm) déjà utilisé en monostatique. La définition des expressions des résolutions pour une image bistatique nous a permis de valider nos résultats et donc notre modèle. Nous considérons enfin la reconstruction d'image pour des scènes plus réalistes telles que les cibles complexes ou la détection de cibles (simples) sur une surface maritime. La comparaison des résultats obtenus dans le cas de l'imagerie monostatique et bistatique montre l'intérêt de cette dernière.The purpose of this work is the study of bistatic radar imaging. In this work, the general case of a bistatic configuration made of moving emitter, receiver and target is considered. It is a full-polarized tri-dimensional model which take into account the all components of the acquisition system. The image reconstruction step is obtained by means of the RDA (Range Doppler Algorithm) algorithm first developed for the monostatic case. According to the defined bistatic resolution expressions of the bistatic image, the proposed model has been validated. Finally, the reconstruction of more realistic scenes like complex targets or the detection of (simple) target on sea surface is considered. The obtained results in the monostatic and in the bistatic cases leads to highlight the interest of the proposed bistatic systems for radar imaging.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF

Diffusion Electromagnétique par une Surface Maritime en Présence de Polluants : Comparaison entre Méthodes Rigoureuses et Asymptotiques

International audienceL’objectif de ce papier est d’étudier les variationsde la signature électromagnétique (EM) de la surface maritimeen présence de polluants. Ainsi, nous avons commencé parl’analyse des modifications qu’entraine la présence de polluants(en émulsion ou sous forme d’une couche) sur les caractéristiquesphysiques et géométriques de la surface maritime. Ensuite, enutilisant la méthode FBM (Forward-Backward method), nousavons estimé les coefficients de diffusion EM d’une surfacemaritime (propre ou polluée) observée dans différentesconfigurations. Dans ce cadre, les simulations des coefficients dediffusion sont analysées en fonction de différents paramètresd’acquisition (état de la mer, type de polluant, fréquence,polarisation, angles d'incidence et d’observation,...). Les résultatsobtenus sont également comparés avec ceux obtenus en utilisantdes méthodes asymptotiques (méthode des petites perturbationsSPM, approximation des faibles pentes SSA et le modèle deuxéchelles TSM)

Numerical Simulations of Electromagnetic Signatureof Sea Surface in Presence of Pollutants

International audienceThis paper present a numerical simulation ofelectromagnetic (EM) signature of a sea surface in presence ofpollutants (emulsion and layer). We have applied the rigorousForward-Backward Method (FBM) and compared the resultsobtained with those given by the asymptotic models, the two-scalemodel (TSM) and small-slope approximation (SSA), in severalconfigurations and for different acquisition parameters such as(wind speed, pollutant type, incidence angle, scattering angle,frequency band and polarizations state)

Assessment of Wind Direction Estimation Methods from SAR Images

International audienceWind information on SAR images are essential to characterize a marine environment in offshore or coastal area. More and more applications require high resolution wind field estimation. In this article, classical wind wave direction estimation methods are reviewed as the spectral or gradient approaches. In addition, a way to enhance the spectral method with the Radon transform is proposed. The aim of this document is to determine which method provides greatest results when the resolution grid is finer. Therefore, the methods accuracy, fidelity and uncertainty are compared through a simulation study, a section with RadarSAT2 data in coastal area and another one with Sentinel-1 measurements in offshore area

Modeling of Bistatic EM Scattering by Polluted Sea Surface UsingAsymptotic and Rigorous Methods

International audienceThis paper presents the study and analysis of the bistatic electromagnetic (EM)signature variation of the sea surface contaminated by pollutants. Therefore, we startwith the numerical analysis the effect of the presence of the pollutant on the sea surfacecharacteristics. Then, we evaluate the EM scattering coefficients of the clean andpolluted sea observed in bistatic configuration by using the rigorous Forward-BackwardMethod (FBM) and the asymptotic Two Scale Model (TSM). The obtained numericalresults of the EM scattering coefficients are studied and given as a function of variousparameters: sea state, type of pollutant, incident and observation angles, frequencies andradar polarization

Bistatic scattering from a contaminated sea surface observed in C, X and Ku bands

International audienceThe aim of the work presented in this paper focuses on the study and analysis of variations of the bistatic electromagnetic signature of the sea surface contaminated by pollutants. Therefore, we will start the numerical analyses of the pollutant effect on the geometrical and physical characteristics of sea surface. Then, we will evaluate the electromagnetic (EM) scattering coefficients of the clean and polluted sea surface observed in bistatic configuration by using the numerical Forward-Backward Method (FBM). The obtained numerical results of the electromagnetic scattering coefficients are studied and given as a function of various parameters: sea state, wind velocity, type of pollutant (sea surface polluted by oil emulsion, and sea surface covered by oil layer), incidence and scattering angles, frequencies bands (C, X and Ku) and radar polarization

Electromagnetic characterization of a polluted maritime surface

International audienceThe objective of this paper is to analyze the effect of the pollutant such as petrol-emulsion on the electromagnetic scattered filed by a maritime surface. Firstly, we investigate the pollutant influence on the maritime surface and physical properties of seawater. Then, we simulate the variation of electromagnetic scattering of the clean maritime surface and also the polluted surface. In this study, the clean and polluted seas are modeled using a semi-empirical spectrum. The simulations of scattering coefficients are realized by using the Forward-Backward Method (FBM), the Composite Two Scale-Model (CTSM) and the Small Slope Approximation (SSA) in monostatic and bistatic configurations. The effect of the pollutant on the electromagnetic scattering of a maritime surface has been studied as function of oil percentage, angles, frequency values and polarization state